Ethylene-butene-2 alternating copolymer

Alternating copolymers of ethylene with olefins containing double bonds in the cis configuration, like ds-2-butene, cyclopentene, cycloheptene,115 and norbomene,116 have been described. Recently also copolymers of carbon monoxide with styrene and styrene derivatives, having syndiotactic117 and isotactic118 configurations, have been synthesized and characterized. 

Figure 2.18 Four possible configurations in chain of alternating copolymer between ethylene and cw-2-butene. Sequences of (+) and (—) bonds are also indicated. Note that in Ref. 119 relative configurations racemo and meso were defined as threo and erythro, respectively.

Corradini, P., and P. Ganis X-Ray Study of the Structure of the Alternated Copolymer Ethylene-cis-butene-2. Makromolekulare Chem. 62, 97 (1963). 

Preferred olefins in the polymerisation are one or more of ethylene, propylene, 1-butene, 2-butene, 1-hexene, 1-octene, 1-pentene, 1-tetradecene, norbornene and cyclopentene, with ethylene, propylene and cyclopentene. Other monomers that may be used with these catalysts (when it is a Pd(II) complex) to form copolymers with olefins and selected cycloolefins are carbon monoxide (CO) and vinyl ketones of the general formula H2C=CHC(0)R. Carbon monoxide forms alternating copolymers with the various olefins and cycloolefins. 

Polyisoprene on hydrogenation gives a rubber directly—an alternating ethylene-propylene polymer. Polybutadiene can give polyethylene on hydrogenation if it is all 1,4 in structure or a variety of flexible-to-rubbery ethylene-butene copolymers as the 1,2 content of the polybutadiene is increased. These polydiene structures can be incorporated as segments in anionic styrene copolymers. 

The 1,2-disubstituted olefmic monomers will usually not homopolymerize with the Ziegler-Natta catalysts. They can, however, be copolymerized with ethylene and some a-olefins. Due to poorer reactivity, the monomer feed must consist of higher ratios of the 1,2-disubstituted olefins than of the other comonomers. Copolymers of cw-2-butene with ethylene, where portions of the macromolecules are crystalline, form with vanadium-based catalysts. The products have alternating structures, with the pendant methyl groups in erythrodiisotactic arrangements. Similarly, vanadium-based catalysts yield alternating copolymers of ethylene and butadiene, where the butadiene placement is predominantly rm/w-1,4. ... 

HHPP [1,21,45] hydrogenated poiy(2,3 dimethyi)butadiene head-to-head polypropylene (alternating copolymer of ethylene and butene-2). 

The melting temperature-composition relations that were described above were for rapidly crystalhzed samples. This crystallization procedure results in relatively small crystallite sizes. In an alternative procedure the crystallization can be conducted isothermally at elevated temperatures and never cooled prior to fusion. It is then found that the melting temperatures are dependent on the nature of the comonomer.(79) Ethylene butene and hexene copolymers behave similarly to one... 

Alternating copolymers can be formed with many pairs, some quite diverse in nature. These include carbon monoxide with propylene, 1-butene, 1-hexene, norbomene, and styrene [38], tetrafluoroethylene with ethylene, propylene, and isobutylene [40-42], and ethylene with propylene [43] and 1-octene [44, 45]. 

Poly(1-butene co ethylene) n Alternative name for ethylene-butene-copolymer. 

Scheme 24. Synthesis of an alternating copolymer with erythro-di-isotactic structure from cis-2-butene and ethylene.

Ethylene-butene-2 isotactic alternating copolymer trans-polypentenamer... 

The symbol ti applies for the isotactic alternate copolymer of ethylene and butene-2 (fig. 6a) in this case the only symmetry element together with the translation is a center of symmetry. 

Randomly incorporated ethylene introduces defects along the backbone. These defects dismpt crystallization, reducing the modulus, melting point, and heat of fusion. The incorporation of random ethylene also reduces haze. Butene has also been used as a comonomer in PP. With the development of metallocene catalysts, even higher a-olefins such as hexene could be incorporated. While these alternative copolymers are now technically feasible, they have not seen commercial... 

It should be added that alternating ethylene/2-butene copolymers can exhibit stereoregularity namely the ethylene/cA-2-butene copolymer, which possesses an erythro-diisotactic structure and is a crystalline polymer. It may be interesting to note that from the formal point of view the alternating eryt/zro-diisotactic ethylene/cA-2-butene copolymer, i.e. erythro-diisotactic poly[ethylene- //-(c/.v-2-butene)], can be treated as isotactic head-to-head and tail-to-tail polypropylene. Isomeric trans-2-bu. ene gives atactic amorphous copolymers with ethylene [2,82]. 

Two compounds of this type were placed at our disposal isotactic polypropylene and an alternating erythro-iso-copolymer of butene-2 and ethylene. Looking to the extended chemical formula of the latter (Figure 13), it is indeed immediately evident that this copolymer can be considered as an equivalent to a HH polypropylene. The XPS analysis of the valence band spectrum of this compound reveals that its electronic structure, reflected through the C-C (C2s) molecular orbitals is entirely different from that of polypropylene (Figure 14). 

Chain propagation of CO/ethylene copolymerization proceeds by a strictly alternating insertion of CO and olefin monomers in the growing chain. It is safe to assume that double CO insertion does not occur for thermodynamic reasons [Ic]. However, the complete absence of double ethylene insertions is remarkable because ethylene insertion in a Pd-alkyl species must be exothermic by about 20 kcal/mol (84 kJ mol). The observation of strict alternation is the more surprising since the same palladium catalysts also efficiently dimerize ethylene to butenes [25]. The perfect alternation is maintained even in the presence of very low concentrations of carbon monoxide. When starting abatch polymerization at a high ethylene/CO ratio, error-free copolymer is produced until all the CO is consumed then the system starts forming butenes (with some catalyst systems at about twice the rate of copolymerization ). 

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